I don't think it is a problem with Scala 3 itself. Scala 3 brought a lot of improvements, one of them is using semantic versioning. People used to complain a log about binary compatibility between versions in 2.x. Now it's here. I think that the slow adoption of Scala 3 is mainly due to one of its most successful projects: Apache Spark. To this day, Spark only supports Scala 2.13 although Scala 3 has been around for years now. This is both disappointing and frustrating because a lot of people were introduced to Scala thanks to Apache Spark.